In the field of tufting, there have been a variety of efforts made to enable both cut pile and loop pile tufts or bights of yarn to be placed in the same row of stitches. In some instances, the structures utilized for this purpose did not allow effective control of the height of stitches and, for instance, the cut pile stitches might always be of greater height than the loop pile stitches. The use of pivoting gate structures on the loopers was proposed in Jolley, U.S. Pat. No. 4,134,347 and Crumbliss, U.S. Pat. No. 4,353,317.
Later sliding gate structures were proposed as typified by Bennett, U.S. Pat. No. 6,155,187. When properly implemented, sliding gate structures may provide rapid response and avoid moving the entire pneumatic activation assembly with the loopers. However, Bennett taught the use of internal biasing elements in pneumatic cylinders and the use of blocks of cylinders to improve efficiencies in assembly. In practice, the use of internal biasing elements limits the size and corresponding force that the biasing elements may provide. In turn, this limits the speed with which the gate can return to the open position after pressure to its corresponding pneumatic cylinder is stopped. Furthermore, the internal biasing elements are not visible to inspection and if rust beings to form due to moisture in the cylinder, for instance, there will be no way to detect the problem until performance degrades to the point where defective carpet patterns are produced, with resulting waste carpet and the need to replace an entire cylinder block rather than merely a spring or biasing element.
Finally, it is desirable to assemble the pneumatic cylinders used to operate the gates in a tight array to permit their use with fine gauge tufting machines. Constructing the cylinders in arrays of removable cylinders stacked four high in nearly vertical columns and designing corresponding gate structures permits this density to be achieved.